Vanessa Redgrave is warm and funny — but seems miscast — in “The Revisionist,” co-starring and written by Jesse Eisenberg. Photo: Sandra Coudert

There are times during “The Revisionist” when you almost have to pinch yourself. Is this actually happening? Are Vanessa Redgrave and Jesse Eisenberg really sharing a stage?

They sure are. Not only that, but the Tony- and Olivier-winning empress of theatah and the rambling prince of “The Social Network” are facing off in a show written by Eisenberg himself — his second after 2011’s “Asuncion.”

The cherry on top of this surreal cake: The two stars aren’t on Broadway but at the 180-seat Cherry Lane Theater, in Greenwich Village.

It’s all too weird — which makes up for a lot since “The Revisionist” isn’t a very good play, and Redgrave maybe wasn’t the right pick for her part.

Make no mistake, she brings a lot of unexpected warmth and humor to Maria, an elderly Pole who hosts her visiting American second cousin, David (Eisenberg), in her cramped, overstuffed apartment.

David has come to the Baltic port of Szczecin to escape distractions and revise the overdue manuscript for his second novel, a supposedly humorous science-fiction allegory. Though this is his first meeting with Maria, he’s barely civil.

Eisenberg’s David is all too familiar since he’s another of the fast-talking, nervously nerdy, hoodie-wearing characters the actor specializes in — though this time the social ineptitude turns into full-blown self-absorption and rudeness.

At times, the cruel portrayal of this empathy-free American novelist is pleasanty uncompromising. But, as a playwright, Eisenberg is unsure of what to do with David — or with Maria, for that matter. The most consistent person on stage is her taxi-driving friend Zenon (Daniel Oreskes, performing almost exclusively in Polish).

And yet this Rattlestick production, directed by Kip Fagan, has its strengths. In a few precious scenes, Eisenberg and Redgrave build an easy rapport despite their starkly different personalities and styles — and the contrast is fascinating. Watching David and Maria amicably munch on pickles, you find yourself dreaming about the show that could have been.